The most common cut used for corned beef is brisket, which is located in the front of the cow near its front legs. Butchers make two different cuts of brisket for corned beef: flat cut and point cut. Another cut used for corned beef is the round.
A point cut brisket comes to a point at an end. The cut has more fat in it, which releases more juices while cooking. It is a good choice to purchase for shredding the beef after cooking. The flat cut is more popular and is much leaner, but still has a layer of fat underneath. Most pre-packaged corned beef kits that come with seasoning and vegetables are flat cut.
Using the round cut produces a leaner overall product, which makes it easier to slice into cuts for sandwiches.